The present invention is directed generally to power control systems and more particularly to phase controlled regulators.
The concept of phase controlled regulation is well known in the art. For example, in U.S. Pat. No. 4,086,526 to Grudelbach a method of and a power switching device for regulating the electrical power delivered to a consumer in an AC network is disclosed. The method includes turning a switching device on at the beginning of each half-wave of the line voltage substantially at a phase angle of zero degrees and turning the power switching device off at a phase angle corresponding to the desired current flow angle.
It is known, however, that AC line voltages fluctuate over time. Various prior art phase controlled regulators which merely connect and disconnect a load to line voltage in response to the phase angle do not compensate for these voltage fluctuations. Therefore, when the voltage is higher than nominal line voltage more power is delivered to the load and when the voltage is lower than nominal line voltage less power is delivered to the load. In numerous applications, this variation in delivered power is not important. However, in certain applications such as where the load includes a lamp, it is known that even small variations in delivered power result in large variations in illumination intensity. Therefore, in certain applications it is desirable to not only connect and disconnect the load to line voltage in response to phase angle information, but it is also important to control the amount of power delivered to the load such that it remains constant.
In U.S. Pat. No. 4,004,214 to Evans a phase controlled voltage regulator is disclosed which delivers substantially constant RMS output voltage to a load from a line voltage which may fluctuate. The Evans patent discloses a timing circuit for operating a switch such as a triac. The timing circuit is responsive to a zero crossing detector. The timing circuit times out a predetermined time period based on the zero crossings of the AC line voltage before rendering the triac conductive. A nonlinear function generator is responsive to the fluctuations in the line voltage. The timing circuit is also responsive to the nonlinear function generator such that the predetermined time period is adjusted based on the magnitude of the line voltage. In this manner, the firing of the triac may be controlled such that substantially constant RMS output voltage is delivered to the load.
Despite the availability of circuits such as that disclosed in the Evans patent, it remains desirable to provide phase controlled regulators which are comprised of a minimum number of low cost components. Lower component counts result in ease of manufacturing, especially using mass production techniques, as well as lower costs to the consumer. Additionally, by using a minimum number of components the overall circuitry can be simplified thus leading to greater reliability.